1. Field of the Invention
The present disclosure relates generally to power converters with synchronous rectification, and more particularly to methods and circuits for improving power converter efficiency.
2. Description of the Related Art
Rectifier circuits have many uses, notably as AC-to-DC power converters. Synchronous rectifier configurations aim to improve the power efficiency of power converters and have been widely adopted in low voltage (<40 V) converters.
Power factor correction (PFC) converters traditionally employ a boost converter with current wave shaping based on input voltage following. FIG. 1 depicts a traditional rectifier circuit including a power factor correction circuit. The PFC boost circuit 100 of FIG. 1 includes a PFC controller 125, gate driver 130, switch 135 and diode 140 to provide rectified voltage to a load 150. Other components illustrated in FIG. 1 include an AC main source 105, a mains voltage diode rectifier circuit 110, filter capacitor 115, inductor 120 and load capacitor 145. Diode 140 has high recovery losses compounded by the high switching frequency (typically 25-100 kHz). Many engineers have tried to design circuits that reduce the impact of reverse-recovery losses on the losses of the converter, but the resulting circuits add cost and complexity to the converter. Most PFC converters cannot absorb this cost and as such these ideas are not generally adopted.
The operation of the FIG. 1 rectifier circuit is primarily in the continuous conduction mode. As a result, operation will become discontinuous near the zero voltage crossing of the AC main source from which power is received due to insufficient voltage to generate sufficient inductor current for self commutation. Traditional PFC controllers 125 are designed to only drive a single switch, such as switch 135, and use a high frequency diode rectifier such as diode 140.
There is a desire for a power factor corrected rectifier that provides improved efficiency, without adding undesired cost and complexity. In addition, there is a desire for a power rectifier that reduces the impact of reverse-recovery losses.